Fig. 4: Mechanisms enhancing luminescence in mechanoluminescent films via hierarchical multiscale structures.

a Schematic illustration of stress directions on micropillar arrays during detachment from the SU-8 template. b Finite-element simulation of stress distribution in a single convex micropillar under tensile loading. c Results during 11 s of cyclic operation: variation of film ML intensity at the emission peak (521 nm) under cyclic loading, displacements of the film in the X- and Z-directions, device velocity along the X-direction, and a schematic of the testing system. d Stress distribution in PDMS films with convex micropillar arrays under static conditions visualized by stress birefringence imaging. e Stress distribution in PDMS films with convex micropillar arrays under tensile loading visualized by stress birefringence imaging. f Comparison of films with hierarchical multiscale and microscale structures: luminescent images (left), SEM images (middle), and SEM of nanoscale surface patterns (right). g ML intensity comparison for films with hierarchical multiscale structures versus microscale structures. Scale bars, 80 µm (d, e); 1 mm (f, left); 100 µm (f, middle); 1 µm (f, right). Source data are provided as a Source Data file.